The invention generally relates to channels used by multiple users in a wireless code division multiple access spread spectrum system. More specifically, the invention relates to a system and method of prioritizing and controlling the flow of data for common and shared channels in a spread spectrum system.
FIG. 1 illustrates a simplified wireless spread spectrum code division multiple access (CDMA) communication system 18. A node b 26 within the system 18 communicates with associated user equipment 20-24 (UE). The node b 26 has a single site controller (SC) 30 associated with either a single (shown in FIG. 1) or multiple base stations 28. A Group of node bs 26, 32, 34 is connected to a radio network controller (RNC) 36. To transfer communications between RNCs 36-40, an interface between the RNCs (IUR) 42 is utilized. Each RNC 36-40 is connected to a mobile switching center (MSC) 44 which in turn is connected to the core network 46.
To communicate within the system 18, many types of communication channels are used, such as dedicated, shared and common. Dedicated channels transfer data between a node b 26 and a particular UE 20-24. Common and shared channels are used by multiple UEs 20-24 or users. All of these channels carry a variety of data including traffic, control and signaling data.
Since shared and common channels carry data for different users, data is sent using protocol data units (PDUs) or packets. As shown in FIG. 2, to regulate the flow of data from differing sources 48-52 into a channel 56, a controller 54 is used.
One common channel used for transmitting data to the UEs 20-24 is the forward access common channel (FACH) 58. As shown in FIG. 3, the FACH 58 originates in a RNC 36 and is sent to a node b 28-34 for wireless transmission as a spread spectrum signal to the UEs 20-24. The FACH 58 carriers several data types from various sources, such as a common control channel (CCCH), dedicated control and traffic channel (DCCH and DTCH), and a downlink and uplink share channel (DSCH and USCH) control signaling. The FACH 58 also carries control signaling out of band, such as hybrid automatic repeat request (H-ARQ), and similar data transmitted via the IUR 62 from other RNCs 38-40, such as CCCH, DCCH, DTCH and H-ARQ control data.
Various controllers are used by the RNC 36 to control the flow of data. A radio link controller (RLC) 64 handles the CCCH. The dedicated medium access controller (MAC-d) 66 handles the DCCH, the DTCH and some out of band H-ARQ signaling. The shared medium access controller (MAC-sh) 68 handles the DSCH, USCH control signaling and out of band H-ARQ control signaling. Controlling the FACH 58 is the common medium access controller (MAC-c) 60.
Due to the multiple sources of data 48-52 that can be transmitted over a common or shared channel, the channel controllers 54 queue the data prior to transmission. If a large backlog develops in the queue, data in the queue develops a latency. A large latency of certain data such as control data will result in the failure of a channel. To alleviate this problem, the prior art either flushed the queue to reduce congestion or rerouted the data. Flushing the queue results in the loss of data and requires retransmission which is undesirable. Rerouting data already queued creates a duplication of data within the system and does not resolve the existing congestion. According, it is desirable to reduce the latency of data for shared and common channels without the problems associated with the prior art.